Wednesday, September 7, 2011

Bacterial resistance to antibiotics

Bacterial resistance to antibiotics is subdivided into two categories,
innate and acquired. Innate resistance is attributed to physiological factors
inherently present in the bacteria rendering it immune to certain
antibiotics.
Acquired resistance is driven by two genetic processes in bacteria:
• Mutation and selection (sometimes referred to as vertical
evolution);
• Exchange of genes between strains and species (sometimes called
horizontal evolution). Some bacterial species are able to spread
drug resistance to other strains and species during genetic exchange
processes.
A number of resistance genes have been associated with large
transferable, extrachromosomal DNA elements; called plasmids, on
which many other mobile elements; termed transposons and integrons
are present.
These DNA mobile elements have been shown to possess genetic
determinants for several different antibiotic resistance mechanisms are
largely responsible for the rapid dissemination of resistance genes among different bacterial genera and species.
Bacterial resistance to antibiotics is manifested by changes in
antibiotic permeability, alteration of target molecules, enzymatic
degradation of the antibiotics, and efflux of antimicrobials from the
cytoplasm. Bacteria use all of these mechanisms to evade the toxic effects
of antibiotics.
The goal of antimicrobial susceptibility testing is to provide
physicians with data that will assist them in choosing the optimal
antimicrobial agent to treat an infection in a patient. Susceptibility testing
in most clinical microbiology laboratories represents a combination of
phenotypic assays that provide either qualitative results (susceptible,
intermediate, or resistant) for a series of antimicrobial agents, or
quantitative results (MICs) that can guide dosing regimens. Molecular-
based tests, such as real-time PCR, may provide rapid information on the
presence of MRSA or VRE in patients, which will assist in infection
control decisions.
Hospital infection control programs are seen as very important for the
control of antibiotic-resistant organisms. Other considerations for an
infection control program include antibiotic control programs and
surveillance systems for infections with nosocomial pathogens.This type
of surveillance is essential for establishing endemic rates.